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Insect minions banned from breeding by same signal

By Aviva Hope Rutkin

No procreating for you, minions

(Image: Alex Wild – http://www.alexanderwild.com/)

Minions, don’t you dare have sex. Queen insects produce a newly discovered pheromone that tells their workers not to reproduce. The pheromone is about 145 million years old and was probably inherited from the insects’ common ancestor.

Insects like honeybees are eusocial, which means that the queens are the only ones in the nest who procreate. The workers’ ovaries don’t develop and they remain sterile. It may seem like the workers get the short end of the stick, but if the nest is thriving, this approach works for everyone. Because the workers are all closely related, they can preserve their own genes by working for the greater good of the nest.

Nevertheless, from an evolutionary standpoint it is hard to understand how eusocial behaviour started. After all, why would any animal evolve behaviours that encourage it not to reproduce? “Since Darwin, there were questions about how this worked,” says Michel Chapuisat at the University of Lausanne in Switzerland.

Anti-sex hydrocarbon

They found that most of the queens produced similar long-chained hydrocarbons, in far greater quantities than the workers did. When the team exposed wasp workers to a synthetic version of the compound, the workers’ ovaries didn’t develop, even though no queen was nearby. Worker ants and bees also failed to develop their ovaries and remained infertile around the chemical.

Ants, wasps and bumblebees all belong to the same family of insects, called Hymenoptera. That suggests they all inherited the pheromone from the common ancestor of the three groups, which lived around 145 million years ago in the early Cretaceous period.

However, it is still unclear how or why that ancient insect evolved this pheromone. The first hymenopterans lived alone rather than in groups, so the researchers think the pheromone was used as an early signal for fertility. It might have been directed at possible male mates, or as a deterrent to other females.

That could help explain how the insects became more social over time&colon; daughters would respond to signals from fertile mothers, remaining sterile and helping to care for other young.

Alternatively, the three insect groups could have evolved the pheromone independently, as they were all exposed to similar evolutionary pressures. “It is still very speculative,” says Van Oystaeyen.